In Spark, John J. Ratey, MD, addresses the mind-body connection, presenting new research in an effort to prove that exercise is truly the best defense against everything from mood disorders to ADHD to addiction to menopause to Alzheimer's. He explains that the brain works just as muscles do-growing with use, withering with inactivity-and shows why getting your heart and lungs pumping can mean the difference between a calm, focused mind and a harried, inattentive self.